GUANTANAMO BAY, Cuba — Evil 9/11 mastermind Khalid Sheik Mohammed will be allowed to dress up like a soldier for his military trial next year — and could even shame the proceedings by wearing an American uniform.

At a pretrial hearing yesterday at Guantanamo Bay, a military judge cleared the way for the admitted mass murderer to wear camouflage clothing at his trial for the Sept. 11, 2001, terror attacks, which killed nearly 3,000 people on American soil.

Although the ruling would forbid the fiendish al Qaeda leader from wearing any present-day US uniform, the judge’s decision doesn’t close the door on Mohammed sticking his arms through the sleeves of an American uniform no longer in use.

Mohammed and his cohorts holed up at the Cuba-based detention center have already made a formal request to wear an American uniform.

In fact, the camouflage-patterned hunting vest pictured in the request bears the label of a US clothing maker, Rothco, which describes itself as America’s foremost wholesale supplier of military and outdoor products.

The request also shows a picture of a similarly camouflaged jacket, but the label is not showing.

Mohammed’s lawyers argued that since he belonged to the mujahedeen militias that the United States financed to overthrow the Soviet-backed communist regime in Afghanistan, he was entitled to wear the camouflage.

“Mr. Mohammed wore a uniform,” said Capt. Jason Wright, one of the defense attorneys.

The military judge, Col. James Pohl, rejected government arguments that the camouflage was inappropriate and could cause security guards to mistake Mohammed for a US serviceman.

The two sides disagreed on the judge’s intent concerning the use of older uniforms.

“The order doesn’t specify past or present,” a commission official said. “It says that ‘the accused may not wear any article of US military clothing.’ That would seem to encompass past and present US military clothing.”

But James Connell, a lawyer for one of the defendants, interpreted the ruling differently.

He said the judge does not specify whether past military uniforms would be permitted. If Mohammed and the others want to wear American uniforms no longer in use, Connell said, “that would have to be sorted out.”

The decision outraged some families of 9/11 victims who were already disappointed at Pohl’s ruling the day before that allows the defendants to skip the pretrial hearings if they wanted.

Mohammed watched the proceedings on a video feed in a nearby holding cell. Defendants Ramzi Binalshibh and Walid bin Attash attended the hearing.

Marty Toyen, of Avon, Conn., whose 24-year-old daughter, Amy, was killed in the World Trade Center attacks, said the camouflage ruling was a slap in the face.

“I don’t consider him a warrior,” Toyen said. “I consider him a terrorist. A warrior fights other warriors. This was an attack against civilians with no warning.”

Merrilly Noeth, of Jackson Heights, Queens, whose son Michael, 30, was killed at the Pentagon, said she caught a glimpse of Mohammed at Monday’s hearing.

“I don’t just have to have nightmares about stick figures anymore,” Noeth said yesterday about finally getting to see Mohammed in the flesh. She was wearing her son’s Navy jacket in court.

The five defendants charged in connection with the attacks of September 11, 2001, who are in hearings this week in Guantanamo, are accused of conspiracy, and six other offenses under the Military Commissions Act.